Satan is in the Old Testament more than people claim. In truth, though, if we look a the “behind the scenes” aspect of the Bible, he’s in all of it.
In Genesis he’s tempting Adam and Eve – saying they can determine their own morality without God. Next, he corrupts the Adamic race to the point where the bonds between the supernatural/normal break and a demonic DNA infestation with fallen angels ensues, bringing on Noah’s Flood.
Satan still isn’t finished as he’s still in the DNA biz, creating more Giants, just as the Israelites are reentering Palestine.
Of course, there’s also the Book of Job, in which Satan is a major player, destroying everything Job has simply to prove that Job supposedly only serves God for the blessings.
Finally there is the Babylonian Exile etc. and though not specifically mentioned, Satan certainly corrupted the Jews to the point where their decadence had to be punished.